Heat treating method and apparatus



June 3, 1969 J. R. BORNOR 3,447,788

HEAT TREATING METHOD AND APPARATUS Filed July 10, 1967 WQWACQ W Q/u/ze Q/cfiard 430/110 M74, Wig m: M

June 3, 1969 J. R. BORNOR HEAT TREATING METHOD AND APPARATUS Sheet 3 M5 Filed July 10, 1967 June 3, 1969 J. R. BORNOR 3,447,738

HEAT TREATING METHOD AND APPARATUS Filed July 10, 1967 Sheet 5 of 5 VSMTQK (7022a Qzc/mz rd Cor/20 & M% W, Val! @WU June 1969 J. R. BORNOR HEAT TREATING METHOD AND APPARATUS Sheet 4 015 MVEZIOTOM Qzc/zard (501-170)" F'iled July 10, 1967 Qji/KG M4 W, Yw'f'? @W/ June 3, 1969 J. R. BORNOR HEAT TREATING METHOD AND APPARATUS Sheet 5 of5 Filed July 10, 1967 oooo o cjh'wromuiyw United States Patent US. Cl. 263-6 Claims ABSTRACT OF THE DISCLOSURE Workpieces to be heated in a furnace chamber and then cooled in a quenching chamber first are introduced into a loading chamber communicating with the furnace and quenching chambers, are shifted into the heating chamber and heated, and then are shifted back into the loading chamber and are transferred to the quenching chamber. To prevent vapors from the quenching chamber and other oxidizing contaminants from entering the furnace chamber, the latter is sealed closed each time the loading chamber is opened to admit new workpieces into the loading chamber or to transfer heated workpieces to the quenching chamber. In addition, the loading chamber is purged with a non-oxidizing atmosphere at such times as it is necessary to open the furnace chamber to shift the workpieces back and forth between the furnace chamber and the loading chamber.

The workpieces are transferred into and out of the furnace chamber by a series of power-driven rollers which also selectively reciprocate the workpieces back and forth Within the furnace chamber to shift the position of the workpieces with respect to heating elements in the chamber and thereby avoid the continuous concentration of heat on the same portions of the workpieces.

BACKGROUND OF THE INVENTION This invention relates to the conditioning of workpieces by first heating the workpieces to high temperatures within a carefully controlled atmosphere in a furnace chamber, and thereafter by cooling the workpieces in a quenching chamber. More particularly, the invention relates to the conditioning of workpieces which are introduced into the furnace chamber through a loading chamber and then are transferred from the furnace chamber to the quenching chamber through the same loading chamber.

SUMMARY OF THE INVENTION The primary object of the present invention is to preserve the integrity of the atmosphere in the furnace chamber both While the workpieces are being introduced into the furnace chamber and while the workpieces are being transferred from the furnace chamber into the quenching chamber. That is to say, the invention aims to prevent contamination of the furnace chamber with either vapors from the quenching chamber or with oxygen from the surrounding environment during such times that the furnace must be open to permit introduction and transfer of the workpieces. For these purposes, the invention contemplates conditioning the workpieces by a novel method which includes keeping the furnace chamber sealed during introduction of the workpieces into the loading chamber, purging the loading chamber with a non-oxidizing gas to prevent impurities in the loading chamber from entering the furnace chamber during admission of the workpieces into the furnace chamber, returning the heated work pieces to the loading chamber while the latter is still in a purged condition, and re-sealing the furnace chamber before transferring the workpieces from the loading chamber to the quenching chamber so as to prevent vapors escaping from the quenching chamber from entering into the furnace chamber during the transfer.

The invention also resides in the provision of improved apparatus for carrying out the novel method in an efiicient and trouble-free manner.

Advantageously, uniform heating of the workpieces is promoted by reciprocating the workpieces back and forth through a limited range within the furnace chamber to prevent the intense heat radiating from heating elements in the chamber from being concentrated continuously on the same particular areas of the workpieces and causing hot spots. In another of its aspects, the invention contemplates novel mechanism which not only reciprocates the workpieces within the furnace chamber but which also transfers the workpieces both into and out of the furnace chamber.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a fragmentary plan view of new and improved conditioning apparatus embodying the features of the present invention.

FIG. 2 is a view similar to FIG. 1 and schematically illustrating the conditioning apparatus.

FIG. 3 is an enlarged fragmentary cross-section taken substantially along the line 3-3 of FIG. 1.

FIG. 4 is an enlarged fragmentary cross-section taken substantially along the line 4-4 of FIG. 1.

FIG. 5 is a fragmentary cross-section taken substantially along the line 5-5 of FIG. 3.

FIG. 6 is an enlarged fragmentary cross-section taken substantially along the line 6-6 of FIG. 3.

FIG. 7 is an elevational view schematically showing the workpieces being reciprocated.

FIG. 8 is a fragmentary perspective view of the reciprocating and transfer mechanism.

FIG. 9 is a schematic view and circuit diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings for purposes of illustration, the invention is embodied in conditioning apparatus for heat treating metal workpieces carried in baskets 10 that are advanced step-by-step through a plurality of conditioning chambers in which the successive steps in the heat treating process are performed to improve the physical properties of the metal of the workpieces. In this instance, the apparatus includes a furnace 11 for preheating the cold workpieces, a high heat furnace 13 for heating the workpieces to a high temperature in a selected atmos pheric condition, and a quenching chamber 14 which is used for cooling the heated workpieces in a water or oil bath. Each basket of workpieces, after first being heated in the preheat furnace 11, is loaded onto a cart 15 and is delivered along a track 16 for transfer into the high heat furnace 13.

The high heat furnace 13 includes an air-tight vessel or shell 17 surrounding an internal enclosure which defines a heating chamber 20 (FIG. 3) and Which is formed by insulated top, bottom and side walls made of refractory material. One of the side Walls is formed with an opening defining a passageway 21 for the admission of each basket into the chamber. Spanning tWo of the other side walls is a hearth (FIGS. 3 and 8) for supporting the basket and herein comprising a plurality of side-by-side ceramic rollers 23 each journaled for rotation about a horizontal axis by means of trunnions 23a bushed in and extending outwardly through the two side walls. Heating of the workpieces to high temperatures while the basket is supported on the hearth rollers is effected by selectively operable radiant heaters such as electric heating tubes 24 (FIG. 3) extending horizontally across the chamber 20 above the rollers. To prevent oxidation of the workpieces during heating, a vacuum pumping apparatus communicating with the vessel 17 and indicated generally at 25 in FIG. 1 evacuates the atmosphere in the vessel and the chamber 20 prior to heating of the workpieces to the maximum temperature.

Upon completion of the heating of the workpieces, the basket is transferred out of the furnace chamber through the passageway 21 and is delivered to the quenching chamber 14. The latter is defined by a walled enclosure formed at one side with an entrance opening 26 (FIG. 5) which is disposed at a right angle to the furnace passageway 21. Each basket delivered into the quenching chamber through the entrance opening 26 is loaded onto spaced parallel rollers 27 (FIG. 4) of an elevator platform 29 and is lowered into a bath of quenching liquid contained in a tank 30 disposed below the opening 26. The platform is cantilevered from an inverted yoke 31 slidable in vertical guide rails 33 within the tank and is raised and lowered in response to the admission of pressure fluid into the opposite ends of a hydraulic actuator 34 connected to the upper end of the yoke. While the basket is immersed in the bath, the quenching liquid is circulated across the workpieces by a submerged pump 35 driven by a motor 36 mounted above the tank 30. After the workpieces have been cooled, the basket is raised out of the i bath by the elevator and is removed from the quenching chamber through an exit opening 37 (FIGS. 2 and 4) which is controlled by a door 38 adapted to be opened and closed by a hydraulic actuator 39. The exit opening 37 is positioned along one side of the track 16, and thus the basket with the treated workpieces may be reloade onto the cart 15 for transfer to a different area.

In accordance with one aspect of the present invention, the furnace chamber 20 and the quenching chamber 14 communicate with each other through a loading chamber 40 (FIGS. 3 and 5) which is utilized in a novel manner to permit introduction of the workpieces into the furnace chamber 20 and to permit transfer of the workpieces from the furnace chamber to the quenching chamber 14 without danger of contaminating the furnace chamber either with the outside atmosphere or with vapors escaping from the quenching chamber. The loading chamber 40 isolates the furnace chamber from the quenching chamber and is purged of oxygen and of vapors from the quenching chamber during such times as it is necessary to open the furnace chamber to introduce and transfer the workpieces. Thus, the admission of an oxidizing atmosphere into the furnace chamber is precluded at all times and, as a result, continuous heating of the furnace chamber may be effected with no danger of contamination of either the parts of the furnace or the workpieces.

In the present instance, the loading chamber 40 is defined by top and bottom walls 41 and 43 (FIG. 3) and four side walls 44 to 47 (FIGS. 3 and 5) and is positioned with the side wall 44 adjacent the quenching chamber 14 and with the side wall adjacent one wall 49 (FIG. 3) of the vacuum vessel 17 so that the three chambers 14, 20, 40 form a generally L-shaped arrangement as shown in FIGS. 1 and 2. The side wall 46 is disposed alongside the track 16 and is formed with an entrance passageway 50 (FIG. 3) through which the baskets 10 may be transferred from the cart 15 into the loading chamber. A door 51 is mounted for up and down sliding across the passageway 50 and may be opened and closed selectively by a hydraulic actuator 53 connected between the door and the upper portion of the side wall 46. Baskets introduced into the loading chamber through the entrance passageway 50 are placed on a conveyor comprising a series of horizontal rollers 54 (FIGS. 3 and 8) extending between the side walls 44 and 47 and formed with trunnions 54a which journal the rollers for rotation about their longitudinal axes. From the loading chamber 40, the workpieces are delivered to the furnace chamber 20 through a passageway 55 (FIG. 3) alined with the passageway 21 of the furnace chamber and defined by an opening formed through the side wall 45 of the loading chamber and the adjacent wall 49 of the vacuum vessel 17. A pair of horizontal rollers 56 (FIG. 8) are disposed between the two passageways 21, 55 to support the baskets as they are moved from the conveyor rollers 54 to the hearth rollers 23.

Advantage is taken of a double door arrangement such as disclosed in the copending application of Harold N. Ipsen, Ser. No. 554,236, filed Apr. 21, 1966, now U.S. Patent No. 3,399,875, to establish an air-tight seal between the loading chamber 40 and the vacuum vessel 17 and to prevent the escape of heat from the furnace chamber 20. Herein, one of the doors is a vacuum door 57 (FIG. 3) formed by a relatively light-weight sheet metal plate disposed within the loading chamber and selectively operable to open and close the passageway 55. The vacuum door is connected by a set of parallel links 59 to a frame 60 which is guided for up and down sliding in channels 61 fastened to the side Walls 44 and 47 of the loading chamber. At its upper end, the frame is attached to the piston rod of a hydraulic actuator 63 mounted on the top wall 41 of the loading chamber. As disclosed more fully in the aforementioned application, the initial downward movement of the frame 60 in response to operation of the actuator 63 causes the vacuum door 57 to move downwardly along the side wall 45 and into alinement with the passageway 55. Continued downward movement of the frame shifts the vacuum door toward the passageway 55 and into tight engagement with the side wall 45 to establish an extremely tight seal between the loading chamber 40 and the vacuum vessel 17. When the frame is shifted upwardly, the vacuum door first is pulled away from the side wall 45 to break the seal and then is lifted upwardly in a path parallel to the side wall 45 thereby to open the passageway 55.

Since the vacuum door 57 is made of light-weight material in order to facilitate opening and closing of the door, it must be protected from the intense heat radiating from the furnace chamber 26 through the passageway 21. For this purpose, a heat door 64 (FIG. 3) made of a thick plate of refractory material is slidable up and down in front of the passageway 21 and is effective not only to shield the vacuum door 57 but also to retain the heat within the furnace chamber. The heat door 64 is operated by a hydraulic actuator 65 and is opened just after opening of the vacuum door and is closed just before closing of the vacuum door so that the latter is always shielded by the heat door and is never exposed to the heat radiating from the passageway 21.

After the workpieces have been heated, the basket 10 is transferred out of the furnace chamber 20 and back into the loading chamber 40 through the passageways 2 1 and 55 and is delivered from the loading chamber into the quenching chamber 14 through a passageway 66 (FIG. 5) defined by an opening formed in the side wall 44 of the loading chamber and alined with the entrance opening 26 in the quenching chamber. A door 67 controlled by a hydraulic actuator 69 mounted on the loading chamber is slidable downwardly across the passageway 66 to seal off the loading chamber from the quenching chamber. To transfer the basket to the quenching chamber, a pusher 70 (FIG. 2 operated by a pneumatic actuator 71 is guided for back and forth reciprocation in the loading chamber in a path extending above and tansversely of the conveyor rollers 54 and is operable to shove the basket from the rollers 54 and onto the elevator rollers 27.

With the foregoing arrangement, a basket 10 is introduced into the loading chamber 40 through the entrance passageway 50 while the door 67 is closed to seal off the quenching chamber 14 and while the double doors 57 and 64 are closed to prevent the outside atmosphere from entering into the furance chamber 20 through the loading chamber. Thereafter, the loading chamber is purged of air admitted by opening of the entrance passageway 50 and of all vapors which previously have entered the loading chamber from the quenching chamber. This is achieved in the present instance by flowing a non-oxidizing gas such as nitrogen or hydrogen into the loading chamber through a pipe 73 (FIG. 2) thereby to drive off the air and vapors in the chamber through an outlet pipe 74. With the loading chamber purged, the double doors 57 and 64 can be opened to permit transfer of the basket into the furance chamber 20 without danger of contaminating the latter chamber with oxidizing gases.

The doors 57 and 64 are closed after transfer of the basket 10, and the furnace chamber 20' is evacuated and raised to a high temperature of approximately 2000 degrees F. At the completion of the heating cycle, the vacuum vessel 17 is pressurized by flowing a non-oxidizing gas into the vessel through a pipe 75 (FIG. 2) in order to break the vacuum and permit opening of the doors 57 and 64. These doors thereafter are opened and the basket is transferred back in the loading chamber 40 while the latter is still in a purged condition to preserve the integrity of the atmosphere in the furance chamber. Before the door 67 leading to the quenching chamber 14 is opened, the double doors 57 and 64 are closed to preclude the possibility of vapors from the quenching chamber entering into the furnace chamber. Finally, the door 67 is opened and the basket 10 is transferred from the loading chamber to the quenching chamber. A new basket then may be introduced into the loading chamber.

From the foregoing, it will be apparent that it is virtually impossible for the furnace chamber 20 to become contaminated with air or vapors since the loading chamber 40 is always maintained in a purged condition when the furnace chamber is open and since the furnace chamber is always sealed when either of the doors 51 or 67 is open. Thus, by purging the loading chamber and by controlling the sequence in which the various doors are opened, the furnace chamber is protected from all contaminating gases. By precluding contaminating gases from the chamber, the workpieces and the parts of the furnace such as the heating tubes 24 will not become oxidized and, as a result, the furnace chamber can be heated continuously. Thus, instead of de-energizing the heating tubes completely between cycles, it is necessary only to reduce the output of the tubes and to lower the furnace chamber to a temperature herein ranging approximately from 900 to 1100 degrees F.

In another of its aspects, the present invention contemplates reciprocating the workpieces back and forth within the furnace chamber 20 to avoid the concentration on the same areas of the workpieces of heat radiating from the heating tubes 24 and thus insure that the Workpieces will be heated uniformly over their entire areas. Moreover, provision is made of a novel drive mechanism 76 (FIG. 8) which is operable to reciprocate the workpieces back and forth within the furnace chamber and which, at the same time, is operable to transfer the workpieces both into and out of the furnace chamber.

To these ends, the hearth rollers 23 are connected to the drive mechanism 76 and are selectively rotated in unison through a predetermined angular distance to advance a basket 10 into and out of the furnace chamber 20 along a path extending through the passageway 21. After the basket has been advanced into the chamber, the rollers are rocked back and forth about their own axes through a shorter angular distance thereby to reciprocate the basket back and forth within the path as shown in FIG. 7 and to shift continuously the areas of the workpieces directly opposing the heating tubes 24.

More specifically, the drive mechanism 76 herein comprises a reversible electric motor 77 (FIG. 7) which is operable to rotate a shaft 79 in a selected direction by means of a worm 80 carried by the drive shaft of the motor and meshing with a worm wheel 81 keyed to the shaft 79, the latter being journaled in bearings 83 (FIG. mounted on a supporting base 84 located adjacent the side wall 47 of the loading chamber 40. In addition to rotating the hearth rollers 23, the drive motor 77 also rotates the conveyor rollers 54, first to advance the basket 10 from the conveyor rollers to the hearth rollers and then to return the basket back into the loading chamber 40 and into alinement with the passageway 66 for transfer into the quenching chamber 14. For this purpose, one end of the shaft 79 is coupled by a drive chain (FIG. 8) to an extension shaft 86 projecting inwardly through the side wall 47 of the loading chamber and connected to the trunnion 54a of the last of the conveyor rollers 54. A series of drive chains 87 are trained around sprockets 89 fast on the trunnions of the remaining conveyor rollers and transmit rotation of the last roller to the other rollers. Thus, as the motor is operated in one direction, the conveyor rollers 54 are rotated clockwise (FIG. 8) to advance the basket onto the hearth rollers 23 and, when the motor is reversed, the rollers 54 are rotated in the opposite direction to pick up the basket as it moves off of the hearth rollers and to move the basket into alinement with the passageway 66.

To rotate the hearth rollers 23, a shaft 90 (FIG. 8) is coupled to the opposite end of the shaft 79 by a magnetic clutch 91 and is connected to the hearth rollers by a drive chain 93. The latter is trained around a sprocket 94 on the free end of an extension shaft 95 projecting inwardly through the vacuum vessel 17 and attached at its other end to the trunnion 23a of the first of the series of hearth rollers. A sealed bearing 96 (FIG. 6) is mounted in the wall of the vacuum vessel and rotatably journals the shaft 95. The drive imparted to the first hearth roller through the chain 93 and the shaft 95 is transmitted to the other hearth rollers by a single endless chain 97 extending around sprockets 98 on the trunnions of the rollers. When the clutch 91 is energized, the motor 77 turns the shaft 90 with the shaft 79 to rotate the hearth rollers and the conveyor rollers through a selected angular distance and in a direction correlated with the direction of the operation of the motor. With this arrangement, a basket may be advanced from the loading chamber 40 and through the passageway 55 by the conveyor rollers 54, picked up by the hearth rollers 23 and advanced through the passageway 21 to a centrally located position in the furnace chamber (see FIG. 3) and, after completion of the heating cycle, returned from the hearth rollers to the conveyor rollers by driving the rollers in the reverse direction.

As shown in FIG. 8, the drive mechanism 76 also includes a hydraulic actuator 100 for rocking the hearth rollers 23 back and forth through a limited range about their own axes thereby to reciprocate the basket 10 within the furnace chamber 20. Herein, the actuator includes a piston (FIG. 9) 101 which slides back and forth in a cylinder 103 in response to the admission of pressure fluid into opposite ends of the cylinder. A piston rod 104 is carried by the piston and is formed at its free end with a row of rack teeth 105 which mesh with a pinion 106 (FIG. 8) fast on a shaft 107 to rock the latter alternately in opposite directions about its axis as the piston rods is reciprocated back and forth. The shaft 107 is suitably journaled on the supporting base 84 and may be coupled selectively to the shaft 90 upon energization of a magnetic clutch 109 interposed between the two shafts. When the clutch 109 is energized, the rocking motion of the shaft 107 is transmitted to the shaft 90 and then to the hearth rollers 23 through the chains 93 and 97 so that the hearth rollers are rocked about their axes in unison to shift the basket back and forth within the furnace chamber. The workpieces thus are continuously shifted with respect to the heating tubes 24 to avoid the formation of hot spots on the workpieces.

To reverse the direction of operation of the hydraulic actuator 100 at proper intervals and to regulate the length of the stroke of the piston rod 104, a pair of limit switches LS-l and LS2 (FIGS. 8 and 9) mounted on the supporting base 84 control a solenoid 110 which is operable to shift a four-way valve 111 for admitting pressure fluid alternately into opposite ends of the cylinder 103 from a fluid pressure source (not shown). More specifically, energization of the solenoid shifts the valve to one position to admit pressure fluid into the head end of the cylinder and thus extend the piston rod, and de-energization of the solenoid results in a spring 113 returning the valve to its initial position to admit pressure fluid into the rod end of the cylinder and retract the piston rod. After a basket has been advanced onto the hearth rollers 23 and properly positioned in the furnace chamber 20, a switch 114 is closed by an automatic control (not shown) which is responsive to the position of the basket. Through the normally closed limit switch LS1, a relay 115 is energized to close a normally open switch 116 and to close a switch 117 setting up a holding circuit for the relay through the normally closed limit switch LS-Z.

Closure of the switch 116 results in energization of the solenoid 110 which shifts the valve 111 to start the piston rod 104 through its forward stroke. As the piston rod shifts forwardly, it engages and moves under the switch operator 119 of the limit switch LS-1 to open the latter switch. The relay 115, however, remains energized through the holding circuit set up by switch 117 and keeps the solenoid energized through the switch 116. Continued forward shifting of the piston rod results in the engagement of the end of the rod with the operator 120 of the limit switch LS-Z whereby the latter switch is opened. At this time, the relay is de-energized to open the switch 116 and de-energize the solenoid. As a result, the spring 113 shifts the valve to admit pressure fluid into the rod end of the cylinder 103 and thus retract the piston rod. Thereafter, the retracting rod moves away from the operator 120 to allow the limit switch LS2 to close idly preparatory to the next cycle. As the piston rod nears the end of its retract stroke, it moves from beneath the switch operator 119 to permit re-closure of the limit switch LS-1 and thereby once again energize the solenoid 110 to reverse the direction of movement of the rod.

Advantageously, the clutch 109 is de-energized to uncouple the shafts 90 and 107 when the basket 10 is being advanced into and out of the furnace chamber by the motor 77 so that the hydraulic actuator 100 will not retard rotation of the shaft 90. By the same token, the clutch 91 is de-energized when the basket is being reciprocated by the actuator thereby to uncouple the shafts 79 and 90 and to keep the gearing 80, 81 from interfering with the rocking of the shaft 90. Moreover, de-energization of the clutch 91 during rocking of the hearth rollers 23 serves to avoid needless rocking of the conveyor rollers 54. Energization and de-energization of the two clutches at the proper times may be effected by the same positionresponsive control utilized for closing the switch 114.

I claim as my invention:

1. In a method of conditioning a workpiece in apparatus comprising a loading chamber having first, second and third walls each formed with an opening defining a passageway, the loading chamber communicating with an enclosed vacuum furnace chamber through the first passageway and communicating with a quenching chamber through the second passageway, said method comprising the steps of, introducing the workpiece into the loading chamber through the third passageway while the first passageway is sealed gas-tight to protect the furnace chamber from gas admitted through the third passageway, flowing a non-oxidizing gas into the loading chamber with all of the passageways sealed gas-tight to purge the loading chamber of air and vapors, opening the first passageway with the loading chamber purged and while leaving the other two passageways sealed gas-tight and transferring the workpiece into the furnace chamber through the first passageway, sealing the first passageway with a vacuum-tight seal and heating the workpiece in the furnace chamber under conditions of high vacuum,

opening the first passageway and transferring the workpiece back into the loading chamber through the first passageway while the other two passageways are sealed gas-tight and while the loading chamber is in a purged condition, opening the second passageway after first sealing the first passageway with a gas-tight seal to protect the furnace chamber from vapors escaping from the quenching chamber through the second passageway, and transferring the workpiece to the quenching chamber through the second passageway.

2. In a method of conditioning a workpiece in apparatus comprising a loading chamber having a pair of walls each. formed with an opening defining a passageway, the loading chamber communicating with an enclosed furnace chamber through the first passageway and communicating with a quenching chamber through the second passageway, said method comprising the steps of, introducing the workpiece into the loading chamber while the first passageway is sealed gas-tight to protect the furnace chamber from gas admitted into the loading chamber as an incident to the introduction of the workpiece, purging the loading chamber of oxidizing air and vapors with both passageways sealed gas-tight, opening the first passageway while leaving the other passageway sealed gas-tight and transferring the workpiece into the furnace chamber through the first passageway, sealing the first passageway with a gas-tight seal and heating the workpiece to a predetermined temperature in the furnace chamber under a selected atmospheric condition, opening the first passageway and transferring the workpiece back into the loading chamber through the first passageway while the second passageway is sealed gas-tight and while the loading chamber is in a purged condition, opening the second passageway after first sealing the first passageway with a gastight seal to protect the furnace chambers from vapors escaping from the quenching chamber through the second passageway, and transferring the workpiece from the loading chamber to the quenching chamber through the second passageway.

3. A method as defined in claim 2 in which the furnace chamber is heated continuously during the times the workpiece is being transferred into and out of the furnace chamber.

4. A method as defined in claim 2 in which the furnace chamber is maintained at a temperature of about 1000 degrees F. when the workpiece is being transferred into the furnace chamber and is raised to a temperature of about 2000 degrees F. after theworkpiece has been transferred into the furnace chamber.

5. Vacuum heat treating apparatus comprising a loading chamber defined by top and bottom walls and a plurality of side walls, a vacuum furnace defining an enclosed heating chamber and communicating with said loading chamber through an opening in a first one of said loading chamber walls, a housing defining a quenching chamber and communicating with said loading chamber through an opening in a second one of said loading chamber walls, a third one of said loading chamber walls having an opening whereby work may be introduced into the loading chamber through said opening in said third wall and selectively transferred to said heating chamber and said quenching chamber respectively through the openings in said first and second walls, three doors, one for each of said openings and each being selectively operable to close and seal its respective opening with a gas-tight seal, means for evacuating the atmosphere in said heating chamber to a condition of high vacuum, and means for flowing a nonoxidizing gas into said loading chamber while all three of said doors are sealed with a gas-tight seal thereby to purge the loading chamber of air and vapors before transferring the work from the loading chamber to said heating chamber.

6. Heat treating apparatus as defined in claim 5 in which said chambers form an L-shaped arrangement with said loading chamber being disposed in the corner of the L, said quenching chamber being formed with an exit opening located on the same side of the L as the opening in said third wall.

7. Heat treating apparatus as defined in claim 5 including a first series of parallel rollers journaled for rotation about horizontal axes in said heating chamber, a second series of parallel rollers journaled for rotation about horizontal axes in said loading chamber, each series of rollers being alined with the opening in said first wall, mechanism coupled to each series of rollers for rotating the rollers in one direction to advance a workpiece from said loading chamber to said heating chamber through the opening in said first wall, said mechanism being selectively reversible to rotate the rollers in the opposite direction to return the workpiece oppositely from said heating chamber to said loading chamber through the opening in said first wall, and means connected to said first series of rollers for rocking the latter back and forth through short arcs to reciprocate the workpiece in opposite directions within said heating chamber.

8. In a heat treating furnace, the combination of, a first walled enclosure defining a heating chamber having an opening, a second walled enclosure defining a loading chamber communicating with said opening, first and second series of side-by-side workpiece-supporting rollers journaled for rotation about horizontal axes in said heating chamber and said loading chamber, respectively, with each series being alined with said opening, drive mechanism including a motor coupled to each series of rollers for rotating the latter in one direction through selected angular distances to advance a workpiece from said loading chamber to said heating chamber through said opening, said drive mechanism being selectively reversible to rotate the rollers in the opposite direction through selected angular distances to return the workpiece oppositely from said heating chamber to said loading chamber through said opening, and means selectively operable to rock the rollers of said first series back and forth through shorter angular distances whereby the workpiece may be reciprocated back and forth within said heating chamber.

9. A heat treating furnace as defined in claim 8 in which said means include an actuator having a reciprocating piston rod shiftable back and forth through a predetermined stroke and coupled to said rollers of said first series.

10. A heat treating furnace as defined in claim 9 in which said motor and said piston rod are coupled to a shaft drivingly connected to the rollers of said first series, and further including a pair of clutches selectively operable to uncouple said motor and said piston rod from said shaft.

References Cited UNITED STATES PATENTS 266-4 1/1957 Wingate 266-4 JOHN J. CAMBY, Primary Examiner.

US. Cl. X.R. 2634 

